Table 7332 Capacity Of Filter Types

SS Removal

Filter Type? Capacity (lb per sq ft)

Surface filtration, septum or leaf Ak to Af

Single-layer granular, sand or coal Af to As

Mixed or dual-layer, sand and coal As to 1

Multilayered with coarse top layer (and upflow type) 1 to 2

Deep, high-rate, coarse media without chemical flocs As to 2

Note: aValues are based on 2 to 3 ft deep beds. For deeper layers or beds, the solids removal capacity increases by 0.5 lb per ft of additional coarse layer.

limit, or (3) the runs are based on time or volumetric throughput.

If air scouring is not included, the endpoint head loss should be restricted to 5 ft or less because higher pressure drops cause hard cakes and mud-balls to form that do not break up with ordinary backwashing. With dual or mul-tilayered beds, the effluent turbidity often reaches unacceptable levels before any significant head loss is detected. Therefore, effluent turbidity monitoring is often required to signal the endpoint.

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